I have a personal theory about this (and certainly have my fair share of experience).
I'm by no means questioning the validity of the information as posted by
@scrappy_underdog i.e. ALWAYS a possibility.
But (and I've brought this up before on another thread): is it just not possible that on different days your own mood (and whatever else goes with creating "mood") has something to do with it? I don't really have the answer i.e. like I said it's just a theory. But it's based on the fact that I've enjoyed booze (binge drinking) most all of my life. Without exception (like when sitting down to a lunch) that first drink (no matter what it is) either "hits the spot" (and I know it's going to be a good session right there and then) or it doesn't (and when it doesn't it doesn't matter HOW much I've thrown down my throat I've just not had a good time or gotten "on" and for no lack of trying on my part I assure you). Had the same with crack (and sometimes even from the exact same rock IF, by some VERY remote chance, which I'll admit was an EXTREMELY rare occasion, there was something left over from the night before) and even although there's no way one can say that there is NO effect from crack (regardless of mood): it's either a GREAT experience and a "bell ringer" or it's a "meh" and "fuck it couldn't be bothered to have another hit" type of thing. Dunno if there's a pharmacological explanation for this. Just something I used to notice is all.